1. Field of the Invention
The present invention relates generally to novel air core gauges employing magnetic field techniques and particularly to air-core gauges and magnetic field techniques therefor which control orienting radially magnetized rotors over an infinite number of angular displacements.
2. Description of the Prior Art
A problem exists in the prior art in forming low profile air-core gauges. Most air-core gauges employ cross-coil arrangements whereby one cross-coil affects interaction with the magnetic rotor differently than the other cross-coil since the magnetic proximity to the rotor of the two coils differ. Reissued U.S. Pat. No. 32,604 dated Feb. 16, 1988 of A. L. Reenstra describes such a coil arrangement. Such a coil arrangement appears to not address the issue of providing a low profile gauge.
A U.S. Pat. No. 4,922,726 dated Feb. 12, 1991 entitled "Woven Crossed-Coil Air-Core Gauge" of Markow, et al. teaches a compact air-core gauge having interlaced stator windings. Such an arrangement yields interchangeable cross-coils which equally effect interaction with the magnetic rotor. Such an arrangement virtually eliminates any positional errors due to unbalanced stato winding fields and it also provides a low profile gauge.
In stepper motor art, 90 degree permanent magnet (PM) step motors have radially magnetized rotors which rotate into alignment with the energized stator winding(s). Such devices appear suitable for accurately positioning and holding loads in the stepped position without the use of encoders or other feedback devices. It makes discrete angular steps rather than an infinite variety of angular displacements as in air-core gauges. Magnetic fields in step motors change quickly when starting, stopping and reversing direction of the rotor. Step motors provide a wide range of rotating speeds directly proportional to the frequency of the input pulse signals rather than to changes in phase and magnitude of complementary analog signals. Step motors align rotors with magnetic poles while air-core gauges align rotors with magnetic fields.
Since most step motors require high torque, rotor pole strength (+m and -m) separated by a distance (L) and the field intensity (H) of the stator coil windings must be high relative to the rotor pole strength and stator field intensity of the air-core gauge. The magnetic moment of a magnet (M) equals m*L. The torque acting on a magnet of magnetic moment M units in a field of intensity of H oersteds is (mHL*sin K), where K equals the angle which the magnet rotor makes with the line of force of the field H. Magnetic moment and field intensity in air-core gauges would be drastically different from those of step motors since ferrite material is not used to concentrate magnetic fields in the coils.
The step motor uses, in most cases, a ferrite stator winding core form to generate high H's while the air-core gauge uses non-metallic core forms. The ferrite cores used in stepper motors to increase flux density tend to distort the fields when used in air-core gauges. This field distortion causes inaccurate pointer deflection angles. Therefore, air-core gauge geometry must be optimized to provide maximum field strength without ferrite cores.